The present invention relates to a surge detection circuit, and more particularly, to a sensor surge detection circuit for detecting surge applied from a sensor to a chip.
Sensors are used in various fields. Sensors have been miniaturized and thus tend to have smaller outputs. Such a sensor is often used together with a detection circuit for detecting the sensor output. The sensor may generate surge when subjected to stress or a sudden temperature change. It is this necessary to prevent the inner circuitry of a chip to which the sensor is connected from being damaged by surges.
FIG. 1 is a schematic circuit block diagram showing surge protection circuits 3a and 3b mounted on a conventional semiconductor chip 4.
A sensor 1 is connected to the semiconductor chip 4 via input terminals 5a and 5b. An output signal of the sensor 1 is provided via input stage amplifiers 2a and 2b, which are mounted on the chip 4, to a circuit in a subsequent stage (not shown).
The surge protection circuit 3a is connected to an input terminal of the amplifier 2a (input terminal 5a). The surge protection circuit 3b is connected to an input terminal of the amplifier 2b (input terminal 5b). The surge protection circuit 3a includes a diode D1, which has an anode connected to the input terminal 5a and a cathode connected to a high potential power supply VDD, and a diode D2, which has a cathode connected to the input terminal 5a and an anode connected to a low potential power supply GND. The surge protection circuit 3b includes a diode D1, which has an anode connected to the input terminal 5b and a cathode connected to a high potential power supply VDD, and a diode D2, which has a cathode connected to the input terminal 5b and an anode connected to a low potential power supply GND.
A high potential surge applied from the sensor 1 to each of the input terminals 5a and 5b is absorbed by the high potential power supply VDD via the diode D1 of each of the surge protection circuits 3a and 3b. A low potential surge applied from the sensor 1 to each of the input terminals 5a and 5b is absorbed by the low potential power supply GND via the diode D2 of each of the surge protection circuits 3a and 3b. As a result, the amplifiers 2a and 2b are protected against surges.
Japanese Laid-Open Patent Publication No. 6-303445 (refer to FIG. 2) describes a horizontal deflection circuit used in a television receiver. The horizontal deflection circuit prevents surges, such as one-shot pulse inputs, from causing erroneous operation or inflicting damage.
Japanese Laid-Open Patent Publication No. 2004-23576 describes an erroneous operation prevention circuit for preventing noise, such as static electricity or surges, from causing erroneous operations. The erroneous operation prevention circuit includes a pulse detection circuit, which detects a pulse (noise) superimposed on an input signal, a pulse extension circuit, which extends the pulse of the detection signal of the pulse detection circuit, and a level holding circuit, to which the detection signal and the input signal are provided.